Immunology

Introduction of immunological processes in the body

Subjects: Immunology · Systems: Immunological · Tags: Immune, Immunological

Lecture 1

Why is Immunology relevant for a future physician?

Autoimmune Diseases

Transplantation

Cancer treatment

Allergy

Lecture 2: Innate Immunity

Introduction

Although vertebrate organisms have evolved a powerful adaptive immunity which is essential for their survival, these organisms retain an elaborate system of innate immunity. Three main features of the innate immune system are:

1. the active killing of damaged host cells by natural killer (NK) lymphocytes in vertebrate specific. They do not exist in invertebrates, reflecting further evolution of the mechanisms of innate immunity after the emergence of vertebrates.

2. The antigen receptors employed by the cells of innate inmmunity have limited specificity (diversity) and recognize common structures – or a repeated chemical nature– present in foreign antigens and most tyically in bacteria. These pattern recognition receptors (pRR) nevertheless afford the ability to recofnize “non self” from “self”, the hallmark of all types of immunity. In contrast, the key feature of adaptive immunity is a genetic machinery able to produce a hugely diverse repertoire of antigen receptors that can bind with high-affinity and specificity each different antigen. In all vertebrates except the agnathans sea lamprey and hagfish,the antigen receptors of the cells of inate immunity, ie antibodies and T cell receptors, differ from those of the cells of innate immnity not lonly of variants available, and hence specificity, but also in structure.

3. The innate and adaptive immunity of vertebrate organisms are strongly interdependent. The evolutionary more recent adaptive immunity of vertebrates is essential for survival as demonstraded by human or experimental mutatioons in key genes responsible for the development of adaptive immunity. Whether innate immunity is essential for survival of vertebrates is more difficult to assert because the processes of innate immunity are numerous and disparate, hence less amenable to genetic analysis. However, mutations in a number of genes involved in innate immunity impair fitness or resistance to infection. Further, certain cells of innate immunity, ie the macrophages, are required for a full adaptative response and the effector mechanisms of the adaptive response itself rely on other components of the innate immunity, such as complement. Hence, evolution of innate and adaptative immunity after vertebrate radiation displays a strong functional interdependence.

The cells of innate immunity

A number of cell types are involved in the host defense from infection in vertebrate organisms as shown by the wide distribution of pattern recognition receptors or the ability to initiate antiviral responses. Certain types, however, play a proeminent role;

Epithelia

Epithelia provide cover to the external body surface and the linings of the mucosae of internal organs sucha s the gastrointestinal, respiratory and genito-urinary tracts and thus constitute the first barrier to the entrance of microbes into the host organism via the skin, the air, food and water or sexual contact. The architecture of epithelial junctions generally provides an effective barrier against microbial colonisation in addition to which epithelial cells (or specialised groups of epithelial cells) can produce ptent antimicrobial peptides and/or other lysozyme, can initiante an interferon-mediated anti-viral response and express several types of pattern recognition receptors thus initiating inflammatory responses.

Phagocytes

Phagocytes, ie cells with the ability to engulf and digest bacteria and other foreign bodies, are a second major population of cells of the innate immunity. There is a single type of professional phagocyte in D melanogaster, but there are at lease two in mammals including mainly: the neutroṕhil and the monocyte-derived tissue macrophage.

Both the neutrophil and the monocyte are circulating cells and both migrate into tissues at sites of infection in response to chemical gradients of pathogen components toward which these cells can migrate. The neutrophil is a short-lived terminally differentiated cell and the fist phagocyte to meet pathogens that have broken the epithelial barrier and reached the underlying conective tissue. In contrast, the monocyte-derived tissue macrophage is a long-lived cell and can re-enter the circulation.

Alongside bacteria themselves, neutrophils and macrophages trigger the inflammatory tissue response through the release of a vast array of chemotactic and pro- inflammatory cytokines. Dentritic cels are special cells found in a number of tissues, including the skin where they are known as Langherans Cells. They are related to the macrophage lineage, but, rather than being involved in bulk clearance of foreign pathogens, their major function is one of antigen processing and presentation to cells of adaptive immunity, namely, the T- lymphocytes

Disclaimer: For education only. Not medical advice; always follow your institution's guidance.